The present invention relates to a variable focal length lens consisting of a discretely controlled micromirror (DCM) array and operational methods for controlling the DCM array.
A widely used conventional variable focal length system makes use of two refractive lenses. It has complex driving mechanisms to control the relative positions of the refractive lenses. This conventional system also has a slow response time. Alternatively, variable focal length lenses can be made by changing the shape of the lens, as is done in the human eye. This method has been used in lenses made with isotropic liquids. Other lenses have been made of media with an electrically variable refractive index to create either a conventional lens or a gradient index lens by means of a voltage gradient. The electrically variable refractive index allows the focal length of the lenses to be voltage controlled. Among them, the most advanced variable focal length lens is a liquid crystal variable focal length lens, which has a complex mechanism to control the focal length. Its focal length is changed by modulating the refractive index. Unfortunately, it has a slow response time typically on the order of hundreds of milliseconds. Even though the fastest response liquid crystal lens has a response time of tens of milliseconds, it has small focal length variation and low focusing efficiency.
In summary, no variable focusing length lens has provided a fast response time, large focal length variation, high focusing efficiency, and adaptive phase control simultaneously.
To solve the limitations of the conventional variable focal length lens, a micromirror array lens was proposed. The details of the fast-response micromirror array lens are described in J. Boyd and G. Cho, 2003, “Fast-response Variable Focusing micromirror array lens,” Proceeding of SPIE Vol. 5055: 278-286. The micromirror array lens mainly comprises a micromirror array and actuating components, and uses an electrostatic force to control the focal length of the lens. The focal length of the micromirror array lens is varied by varying the displacement of each micromirror. The practical use of the micromirror array lens is limited by the displacement range of the micromirror, high driving voltage, and complex electric circuits. These limitations are caused by establishing equilibrium between the electrostatic force and the elastic force to control the displacement of the micromirror.
To overcome these limitations, the discretely controlled micromirror (DCM) was invented. The details of the DCM are described in the applicant's U.S. patent application Ser. No. 10/872,241 for “Discretely Controlled Micromirror With Multi-Level Positions”, which was filed on Jun. 18, 2004, the disclosure of which is incorporated by reference as if fully set forth herein. The DCM has a large displacement range, has low driving voltage, and is fully compatible with the microelectronics circuits. Two exemplary DCMs were invented, which are a Variably Supported Discretely Controlled Micromirror (VSDCM) and a Segmented Electrode Discretely Controlled Micromirror (SEDCM). The displacements of the VSDCM are determined by supports providing gaps of various width through which the DCM can move. The displacements of the SEDCM are determined by combinations of sizes, positions, and discrete voltages of segmented electrodes.
This invention provides a discretely controlled micromirror array lens (DCMAL) and DCMAL array consisting of DCMs to overcome the limitations of conventional micromirror array lens.